1. Field of the Invention
The present invention generally relates to injection molding machines and methods for protecting the injection molding machines. More particularly, the present invention relates to an injection molding machine, such as an electric injection molding machine or a hybrid type injection molding machine, having a dynamic brake apparatus provided for an electric driving machine used as an actuator for an injection apparatus, a mold clamping apparatus or others, and a method for protecting the injection molding machine.
2. Description of the Related Art
An electric driving machine, such as a motor, is used for an electric injection molding machine as a driving source. The motor is also used for a hybrid type injection molding machine that takes in beneficial points of both hydraulic and electric injection molding machines.
In the above mentioned injection molding machines, the motor is driven so that an injection screw is rotated, advanced, and retracted, a moveable platen is advanced and retracted, and an ejector pin of an ejector apparatus for molded articles is advanced and retracted. In addition, dynamic brake apparatuses are provided for various motors of the injection molding machine, as apparatuses for consuming regenerative electric power of the motors.
FIG. 1 is a schematic structural view of a driving circuit of a motor provided for an electric injection molding machine as an example of a conventional injection molding machine.
Referring to FIG. 1, the driving circuit includes a converter part 2, an inverter part 3, a dynamic brake apparatus 5, and a smoothing capacitor 6.
The converter part 2 converts an alternating current being sent from a three-phase alternating current electric power source 1 to a direct current. The inverter part 3 converts the direct current being sent from the converter part 2 to an alternating current, so that the alternating current is supplied to a motor 4. The dynamic brake apparatus 5 is connected to a DC link part 8 provided between the converter part 2 and the inverter part 3. The capacitor 6 is connected to a part of the DC link part 8 provided between the converter part 2 and the dynamic brake apparatus 5.
The dynamic brake apparatus 5 includes a regenerative resistance part 5-1 and a switch element 5-2. Regenerative electric power of the motor 4 is consumed by the regenerative resistance part 5-1. The switch element 5-2 is on-off controlled by a controller 9. The dynamic brake apparatus 5 functions as an apparatus for consuming the regenerative electric power of the motor 4.
In the above mentioned driving circuit, the rotational speed of the motor 4 is reduced so that the motor 4 is made regenerative and a control signal is output from the controller 9. The switch element 5-2 is on-off controlled by the control signal. If the switch element 5-2 is made xe2x80x9conxe2x80x9d, the regenerative electric power of the motor 4 is consumed by the regenerative resistance part 5-1.
If the regenerative electric power of the motor 4 is high, the dynamic brake apparatus 5 is in an overload state so that the regenerative resistance part 5-1 may be burned. Hence, it is necessary to detect such a overload state and reduce the load on the motor 4 by stopping the operation of the motor 4 or reducing torque or the rotational speed of the motor 4, in order to protect the driving circuit of the motor 4. Because of this, a thermal overload relay 7 is generally provided for the dynamic brake apparatus 5. The thermal overload relay 7 detects that the value of the regenerative electric power of the motor 4 exceeds the designated values. Alternatively, instead of the thermal overload relay 7, an electric current detector or a voltage detector, which is not shown in FIG. 1, detecting that the dynamic brake apparatus 5 is in the overload state, is provided for the dynamic brake apparatus 5.
Meanwhile, it is necessary for the rotational speed of the motor 4 of the above mentioned electric injection molding machine to be controlled to accelerate or decelerate in a short cycle during a process of mold clamping or injection, for example, in order to produce a large number of molded articles in a short period of time efficiently. Because of this, the motor 4 is made regenerative frequently. Therefore, it is very important for the dynamic brake apparatus 5 of the electric injection molding machine to be prevented from being in the overload state due to high regenerative electric power of the motor 4 high, from the point of view that desirable molded articles are produced efficiently.
On the other hand, if a protection exclusive device, such as the above mentioned thermal overload relay 7, the electric current detector, or the voltage detector, is provided in order to protect the dynamic brake apparatus 5 as in the above mentioned conventional electric injection molding machine, a large electric injection molding machine may be required. Such a large machine requires more space and makes manufacturing cost too high.
Accordingly, it is a general object of the present invention to provide a novel and useful injection molding machine having a dynamic brake apparatus provided for an electric driving machine and method for protecting the injection molding machine, in which one or more of the problems described above are eliminated.
Another and more specific object of the present invention is to provide an injection molding machine and a method for protecting the injection molding machine wherein it is realized that the dynamic brake apparatus provided for the electric driving machine, such as motor, used as an actuator is protected from an overload state in a simple structure.
The above objects of the present invention are achieved by an injection molding machine, including an electric driving machine, a dynamic brake apparatus which is provided for the electric driving machine and consumes regenerative electric power of the electric driving machine as a load, and a controller configured to output a driving output signal to the dynamic brake apparatus so as to control that the dynamic brake apparatus consumes the regenerative electric power of the electric driving machine, wherein the controller estimates the load to the dynamic brake apparatus based on the driving output signal output to the dynamic brake apparatus and determines whether or not the dynamic brake apparatus is in an overload state based on the estimated load.
The above objects of the present invention are also achieved by a method for protecting an injection molding machine, comprising the steps of a) estimating a load to a dynamic brake apparatus provided at the injection molding machine, based on a driving signal input to the dynamic brake apparatus, b) determining whether or not the dynamic brake apparatus is in an overload state based on the estimated load, and c) protecting the dynamic brake apparatus, in a case where it is determined that the dynamic brake apparatus is in the overload state and a term wherein the overload state continues exceeds a predetermined term.
According to the present invention as described above, it is possible to determine with a simple structure whether or not the dynamic brake apparatus is in an overload state, in order to protect the dynamic brake apparatus provided for the electric driving machine from the overload state.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.